Ran across this article shows some Forrester Research data that Open Source databases such as PostgreSQL are 60% cheaper than the commercial alternatives.
I think most geeks are already aware of this. What I found interesting is the quote:
"Eighty per cent of the applications typically use only 30 per cent of the features found in commercial databases," Yuhanna told vnunet.com. "The open source databases deliver those features today."
In my experience working with clients it is more like 95% of applications use only 10% of the features found in commercial databases. I can't even count the number of times a company absolutely needed Oracle for a 100MB, 3 table, simple CRUD database.
One of my favorite themes that comes up is when a company again needs Oracle/DB2/whatever because it has all of the mission critical features they need such as clustering, fail over, etc. Then when it comes to implementation time the tune changes to "Oh we don't really need a cluster. And now that I think about it, we can handle downtime easily, so fail over isn't required either."
I think it comes from the fear that they might need those features and so they play a safe bet. Much like when you buy something like a car and get the luggage rack on the roof, "just in case", but then realize years later that you've never used it.
Moral of the story? As with any type of project, even non-technical ones, you should worry the most about what you know you need today and let tomorrow take care of itself. The tomorrow you are worried about may never come.